Internal combustion engines typically have an engine block, typically including cylinders for reciprocating pistons and structure to mount a crankshaft and other elements. Heads are typically placed on the block with a multiplicity of fasteners or studs. A gasket is usually placed between the head and the block, this gasket called a head gasket.
Heads can either be separate or unitary. For example, a unitary head would be a single head which engages a multiplicity of cylinders. For example, in the V-6 or V-8 engine typically found on modern American road cars, there are two heads, one for each bank of cylinders. On a straight 6 engine, however, where the cylinders are aligned along a single longitudinal axis, there may be only one unitary head. However, some large tractors or industrial engines have separate heads for each cylinder.
Repair or maintenance to the internal combustion engine sometimes require removal of the head.
Industrial engines or earth moving equipment engines, for example, the Caterpillar 3500 engine are quite heavy and have separate heads. The Caterpillar 3500 engine is an industrial multi-purpose engine that may be used as a generator or used on drilling rigs or the like. It comes in 8, 12, 16 or 20 cylinder models, all having V blocks and overhead valves.
As may be imagined, the removal of the heads, even though separate heads, on such a large engine, for example, the Caterpillar 3500 Series engine, is difficult. This difficulty is due in part to the weight, location, and design configuration of the blocks.